Metal pickling process



52. GOMPOSITlONS,

Patented June 27, 1933 Hit: 3

UNITED STATES GEORGE L. MAGOUN, OF NITRO, WEST VIRGINIA ASSIGNOR TO THE RUBBER SERVICE LABORATORIES 00., OF AKRON,

OHIO, A CORPORATION OF OHIO v METAL PICKLING PROCESS 80 Drawing.

The present invention relatesto the cleaning and preservation of metallic surfaces, wherein a metal is in contact with a liquid of an acid nature. More particularly, the invention relates to the prevention of excessive pitting and embrittlement of a metal when subjected to a pickling process by treatment with a dilute solution of a mineral acid.

Certain objects of the present invention are to prevent the acid pickle liquor from attacking clean portions of the surface of a metal; to obviate over-pickling, embrittlement and pitting of the articles treated; to minimize the amount of metal lost in pickling; to increase the efiiciency of the pickling operation; to prolong the effective life of the pickling bath; and particularly to facilitate the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

In the art of pickling, the metal is treated with a dilute acid to remove oxides such as 25- rust,*scale,- and other deposits, after which the metallispreferably washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid removes the rust and scale, but unfortunately, from the pickling standpoint, unless some agent to prevent such action is present, it attacks the cleaned metal itself, thereby causing loss of metal and producing an evolution of hydrogen gas, which escapes into the air, carrying with it a fine spray of the acid liquor from the pickling bath and producing an atmosphere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a minimum. To accomplish the objects set forth in accordance with the present invention, there is added to the pickling bath a regulating agent or ingredient which acts to restrain the action of the acid from attacking clean metal. but facilitates the removal of the rust. scale and other deposits, or in other words, the regulator or inhibitor causes the Application filed February 16, 1931. Serial No. 516,209.

acid selectively to remove such materials without appreciably attacking the clean portions of the metal under treatment.

The pickle regulator or inhibitor, as disclosed in the present application, comprises an aromatic amino derivative o f a mercaptoirylthiaig'lf k A" Q Tn the examples hereinafter set forth for carrying out the metal pickling process, conditions were imposed which duplicated, so far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed.

Test pieces of 80 gauge'cold rolled tin plate steel stock, approximately 4"x3" in dimension, were immersed in approximately 750 c. c. of a water solution of sulfuric acid containing approximately 6% by weight of 66 B. acid to which had been added a small quantity of one of the preferred type of inhibitors. The loss in weight of the steel test pieces resulting from maintaining the strips in the pickle bath in the manner described for a definite period of time was then determined. The temperature of the pickling bath was maintained at from 80 to 85 C. For the acid concentration set forth, commercial practice is to pickle at approximately 66 to 88 C. The results so obtained were compared with similar tests wherein the steel pieces were subjected, under the conditions set forth, to the action of an acid solution of the strength and for the time specified above, but containing no inhibitor.

Examples of the preferred class of materials may in general be prepared by heating the amino compound with a mercaptoarylthiazole at altemper'ature suificient to cause reaction. (preferably below 160 (1.).

One method whereby one of the preferred class of compounds, for example, a reaction product of 2 :mercaptobenzothiazole and paraphenylene -diamine wasprepared folows:

Substantially two molecular proportions of Q-mercaptobenzothiazole and substantially one molecular proportion of paraphenylenediamine were placed in a suitable vessel and 100 heated at a temperature of approximately 140 to 150 C. until the reactants were melted together and reacted. The product formed, when cool, was a solid whichreadily ground to a fine powder.

A sample of the product prepared as described above was incorporated in a pickling bath in the manner hereinbefore described. Thus, a steel test piece, 3"x4" in dimension, cut from 30 gauge cold rolled tin plate stock, exposing approximately 24 square inches of surface and weighing 18.442 grams was found to lose but 0.026 grams after 40 minutes pickling in 750 c. c. of a 6% sulfuric acid solution containing 0.04? grams of the inhibiting product hereinbefore described. A similar test piece weighing 18.738 grams and treated in the same manner, but without the use of any inhibitor lost 0.541 grams. Thus it is shown that when the reaction product of 2-mercaptobenzothiazole and para-phenylenediamine is employed as an inhibitor, the loss in weight per square inch of surface exposed corresponds to 0.00108 grams, whereas when no inhibitor is employed in the test described, the loss per square inch of surface exposed corresponds to 0.02254 grams. The loss in weight per square inch of surface exposed is only 4.8 percent as great by employing the inhibitor set forth as results if no inhibitor is employed in the pickling process. A greater saving in metal losses results from the use of a larger amount of the inhibitor than that employed in the example. Moreover, the steel plates pickled in the presence of the inhibitor set forth are clean and not stained upon removal from the bath.

Other aromatic amino derivatives of a mercaptoarylthiazole have been prepared and tested as inhibitors in a pickling bath in the manner hereinbefore described. Except in the case of Compound D. the following compounds were all prepared in the general manner hereinbefore described. The method for the preparation of Compound D is given below.

Compound A.Benzylamine derivative of Q-mercaptobenzothiazole;

Compound B.Reaction product of substantially two molecular proportions of 2- mercaptobenzothiazole and substantially one molecular proportion of 2,4-diamino-diphenylamine.

Compound C.Reaction product of substantially one molecular proportion of 2-mercaptobenzothiazole and substantially one molecular proportion of beta-naphthylamine.

Compound D.Reaction product of substantially three molecular proportions of 2-mercaptobenzothiazo1e and substantially one molecular proportion of 2,4t-diaminodiphenylamine. (This compound was prepared preferably by heating the reactants in the presence of an organic solvent, preferably ethyl alcohol to a temperature of approximately 35 C5.

Compound E.-Reaction product of substantially one molecular proportion of 2-mercaptobenzothiazole and substantially one molecular proportion of para-para-diaminodiphenyl-methane.

Compound F .-Reaction product of substantially one molecular proportion of 2-mercaptobenzothiazole and substantially one molecular proportion of diphenylamine.

The results of the tests obtained on immersing steel test strips of 30 gauge cold rolled tin plate stock, 3"x4" in dimension, for 40 minutes in 750 c. c. of 6% by weight of 66 B. sulfuric acid maintained at a temperature of 85 C., in the presence of 0.047 grams of one of the above described inhibitors, are given in Table I.

Table I Weight w M I weigh}; ('eigh; loss in tee o stee grams Inmhmug iniii bimi sc ri p strip per sq. employed employed before after inch of pickling pickling surface exposed Grams Grams Grams Grams Compound A 0 047 18.021 17. 997 0. 00100 Compound B 0. 047 18.521 18. 493 0. 00117 Compound C 0. 047 18. 645 18.616 0. 00121 Compound D 0. 047 17. 808 17. 778 0. 00125 Compound E 0. 047 18. 416 18. 377 0. 00163 Compound F 0. 047 18. 529 18. 496 0. 00138 None None 18. 738 18. 197 0. 02254 It is thus apparent from the data set forth that the preferred class of materials constitutes an important and highly efficacious group of inhibitors, as in all cases wherein one of the preferred inhibiting compounds was incorporated in the pickle liquor there resulted a great saving in the loss in weight of the steel test strips as compared with that resulting when no inhibitor was employed.

Other examples of the preferred class of inhibitors may be prepared by reacting other aromatic amines, such as aniline, toluidine, methyl-phenyl-amine, -meta-phenylene-di- -itinine, anthramines', and the like, with mercaptobenzothiazoles, mercaptotolylthiazoles, mercaptonaphthiazoles and the like; and the products so formed employed as inhibitors in the pickling bath in the manner hereinbefore set forth.

Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling of metals are apparent to those skilled in the art to which this invention pertains. The products described additionally may be employed in the presence of foaming agents, ionizable substances or other materials ordinarily used, and are employable with the various acids commonly employed commercially in the acid pickling of metals. Thus hydrochloric acid, or other acids employed in the metal cleaning process, may be employed as the pickle acid in con- 252. COMPOSITIONS,

junction with the preferred class of inhibitors hereinbefore set forth.

hat is claimed is:

1. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a substantially non-oxidizing mineral acid solution containing a small proportion of an aromatic primary diamino derivative of a mercaptoarylthiazole.

2. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a reaction product of an aromatic primary amine and a mercaptobenzothiazole.

3. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a reaction product of an aromatic primary diamine and a mercaptobenzothiazole.

4. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a reaction product of a phenylene-diamine and a mercaptobenzothiazole.

5. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a reaction product of para-phenylene-diamine and Q-mercaptobenzothiazole.

6. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of the reaction product of substan- MA A tial ly pne,molecular proportion of paraphenylene-diamine and substantially two molecular proportions of Q-mercaptobenzothiazole.

7. A pickling bath for iron and steel products which comprises a substantially non-oxidizing mineral acid solution containing a small proportion of an aromatic primary diamino derivative of a mercaptoarylthiazole.

8. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a reaction product of an aromatic primary amine and a mercaptobenzothiazole.

9. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a reaction product of an aromatic primary diamine and a mercaptobenzothiazole.

10. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a reaction product of a phenylene-diamine and a mercaptobenzothiazole.

11. A pickling bath for iron and steel roducts which comprises a sulfuric acid soution containing a small proportion of a reaction product of para-phenylene-diamine and Q-mercaptobenzothiazole.

12. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of the reaction product of substantially one molecular proportion of para-phenylene-diamine and substantially two molecular proportions of Q-mercaptobenzothiazole.

13. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of an aromatic primary amino derivative of a mercaptoarylthiazole.

14. A pickling bath for iron and steel products which comprises a mineral acid solution containing a small proportion of an aromatic primary amino derivative of a mercaptoarylthiazole.

In testimony whereof I hereunto afiix my signature.

GEORGE L. MAGOUN. 

